Organic electroluminescent display device and method of manufacturing the same

ABSTRACT

An organic electroluminescent display device including a rear substrate, an organic electroluminescent portion disposed on a surface of the rear substrate, the organic electroluminescent portion including a first electrode, an organic layer, and a second electrode in sequence, a front substrate coupled to the rear substrate at an internal surface of the front substrate to seal an internal space in which the organic electroluminescent portion is accommodated, thereby isolating the organic electroluminescent portion from the outside, a transparent moisture-absorbing layer coated on the internal surface of the front substrate, and a sealant disposed between the rear substrate and the transparent moisture-absorbing layer to couple the front substrate and the rear substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/161,405, filed on Jan. 22, 2014, which is a divisional of U.S.application Ser. No. 11/934,577, filed on Nov. 2, 2007, now U.S. Pat.No. 8,652,566, which is a divisional of prior application Ser. No.10/729,989, filed Dec. 9, 2003, now abandoned, and claims priority toand the benefit of Korean Patent Application No. 10-2003-0023219, filedon Apr. 12, 2003, which are all hereby incorporated by reference for allpurposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent (EL)display device and a method of manufacturing the same, and moreparticularly, to an organic EL display device with an improvedencapsulation structure, and a method of manufacturing the same.

2. Background of the Invention

Generally, organic EL display devices are self-luminescent displaydevices which emit light by electrically exciting a fluorescent organiccompound. They can be operated with low voltage and made thin. Inaddition, organic EL display devices have advantages, such as a wideviewing angle and a fast response speed, that overcome some of theproblems of liquid crystal displays. Accordingly, it is expected thatorganic EL display devices may be applied to next generation displaysthat can overcome some of the shortcomings of liquid crystal displays.

In such organic EL display devices, an organic layer is formed in apredetermined pattern on a substrate made of glass or other transparentinsulators. Electrode layers are disposed above and below the organiclayers. The organic layers are made of organic compounds.

In organic EL display devices having the above-described structure, whenpositive and negative voltages are applied to the electrodes, holes aremoved from an electrode, to which a positive voltage is applied, to anemission layer via a hole transport layer. Electrons are moved from anelectrode, to which a negative voltage is applied, to the emission layervia an electron transport layer. The electrons meet the holes in theemission layer, thereby generating excitons. The excitons make atransition from an excitation state to a ground state, thereby causingfluorescent molecules of the emission layer to emit light. As a result,an image is formed.

In the aforementioned organic EL display devices, moisture absorbed intothe device may result in deterioration of device performance. Thus,organic EL display devices may require an encapsulation structure forpreventing infiltration of moisture.

In conventional organic EL display devices, several encapsulationtechniques have been proposed, including methods in which a metal can ora glass substrate is processed in the form of a cap having a groove towhich a powdered absorbent for absorbing moisture is applied.Alternatively a film of the absorbent is adhered using a double-sidedtape. However, since applying the absorbent to the groove may be quitecomplicated, the material and processing costs may increase, and theoverall thickness of the substrate may increase. In the case of apowdered absorbent, it cannot be used for a front emission type displaydevice since the substrate used for encapsulation is opaque. Meanwhile,in the case of a film-like absorbent, there is a limit to preventing theinfiltration of moisture. Since the film-like absorbent may be easilydamaged due to scratches or other external impacts during manufacture oruse, high durability and reliability cannot be attained. Thus, theencapsulation structure using a film-like absorbent is not generallysuitable for mass production of organic EL display devices.

Japanese Patent Laid-open Publication No. 9-148066 discloses an organicEL display device comprising a laminate in which organic luminescentmaterial layers made of organic compounds are disposed between a pair ofopposite electrodes and within a hermetic container for isolating thelaminate from external air. A drying material is disposed in thehermetic container, wherein the drying material absorbs moisture so thatthe device maintains a solid state even as it absorbs moisture. Examplesof the drying materials include alkali metal oxides, sulfuric salts andthe like. Such an organic EL display device may become bulky due to theshape of a hermetic container. Also, even if the device is maintained ata solid state after absorption of the moisture, the device cannot beused for a front emission type display because of its opacity. Further,since the manufacturing process is complicated, the material cost andprocessing cost may increase.

Japanese Patent Laid-open Publication No. 5-335080 discloses a method offorming a protection film for an organic EL device. In the disclosedmethod, a shapeless silica protection film is formed on an organic ELdevice having an electroluminescent material layer containing at leastone kind of organic compound between positive and negative electrodes,at least one of which is a transparent electrode. In the disclosedorganic EL device, the structure for preventing moisture infiltrationfrom the outside is configured such that dense, shapeless silica isthickly coated on one electrode. However, while the structure cannotabsorb moisture inherently existing in the device, it can protect theorganic EL device from external moisture. Thus, when using shapelesssilica as a protective film material, separate structure for absorbinginherent moisture may be further necessary.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides an organicelectroluminescent (EL) display device having absorbing structure bywhich a transparent state can be maintained so as to allow a frontemission type display even after absorption of moisture. The presentinvention further provides a method of manufacturing the organic ELdisplay device.

A further exemplary embodiment of the present invention provides anorganic EL display device which can simplify the manufacturing process,thereby reducing material and processing costs.

An exemplary embodiment discloses an organic electroluminescent displaydevice including a rear substrate, an organic electroluminescent portiondisposed on a surface of the rear substrate, the organicelectroluminescent portion including a first electrode, an organiclayer, and a second electrode in sequence, a front substrate coupled tothe rear substrate at an internal surface of the front substrate to sealan internal space in which the organic electroluminescent portion isaccommodated, thereby isolating the organic electroluminescent portionfrom the outside, a transparent moisture-absorbing layer coated on theinternal surface of the front substrate, and a sealant disposed betweenthe rear substrate and the transparent moisture-absorbing layer tocouple the front substrate and the rear substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of an organic EL display deviceaccording to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a porous silica layer used in anorganic EL display device according to an embodiment of the presentinvention;

FIGS. 3A through 3D are cross-sectional views of steps in a method ofmanufacturing a single organic EL display device according to anembodiment of the present invention;

FIGS. 4A through 4E are cross-sectional views of steps in a method ofmanufacturing a plurality of organic EL display devices according to anembodiment of the present invention; and

FIG. 5 is a flow diagram illustrating a method of manufacturing anorganic EL display devices according to an embodiment of the presentinvention.

FIG. 6 is a cross-sectional view of an organic EL display deviceaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a cross-sectional view of an organic EL display deviceaccording to an embodiment of the present invention. Referring to FIG.1, an organic EL display device 10 includes a rear substrate 11 made ofglass or a transparent insulator, an organic EL portion 12 formed on onesurface of the rear substrate 11 and having a first electrode, anorganic layer and a second electrode sequentially laminated. A frontsubstrate 13 is coupled to the rear substrate 11 to seal an internalspace 16 in which the organic EL portion 12 is accommodated, forisolating the organic EL portion 12 from the outside. The frontsubstrate 13 has a transparent moisture-absorbing layer 14 coated on itsinternal surface.

The organic EL portion 12 may be formed by sequentially depositing afirst electrode, an organic layer and a second electrode, so that thefirst electrode serves as a positive electrode and the second electrodeserves as a negative electrode. The organic layer may include at leastan emission layer. Also, the organic EL portion 12 may include a firstelectrode as a positive electrode, a hole transport layer, an emissionlayer, an electron transport layer, and a second electrode as a negativeelectrode.

The front substrate 13 may be a glass substrate that is an insulator, atransparent plastic substrate or similar material. In the case of thetransparent plastic substrate, a protection layer for protecting theplastic substrate against moisture may be formed on the internal or theouter surface of the plastic substrate. The protection layer may haveheat resistance, chemical resistance and/or moisture permeationresistance.

For a rear emission type display, the first electrode of the organic ELportion 12 may be a transparent electrode, and the second electrode ofthe organic EL portion 12 may be a reflection-type electrode. For afront emission type display, the first electrode of the organic ELportion 12 may be a reflection-type electrode, and the second electrodeof the organic EL portion 12 may be a transparent electrode. The firstelectrode is disposed near the rear substrate 11, and the secondelectrode is disposed near the front substrate 13.

In order to impart heat resistance, chemical resistance, and/or moisturepermeation resistance, an inorganic protection layer 17 for planarizingthe top surface of the organic EL portion 12 may be further provided onthe second electrode. The protection layer 17 may be made of metaloxide, metal nitride or similar material.

The internal space 16, defined by the front substrate 13 and the rearsubstrate 11, may be made vacuous, or may be filled with an inert gas,e.g., neon, argon, or other gas capable of performing the same functionas the inert gas. The front substrate 13 and the rear substrate 11 aregenerally coupled to each other using a sealant 15.

The moisture-absorbing layer 14 may be a porous silica layer. The poroussilica layer may have a thickness in the range of about 100 nm to about50 μm in view of manufacturing process and performance.

FIG. 2 shows a porous silica layer used as a moisture-absorbing layer inthe organic EL device according to an exemplary embodiment of thepresent invention. Referring to FIG. 2, the porous silica layer 14includes a silica frame 14 a and absorption holes 14 b. The silica frame14 a props up the construction of the porous silica layer 14, and theabsorption holes 14 b absorb moisture. As described above, the poroussilica layer 14 is maintained at a transparent state before and afterabsorption of moisture.

According to an exemplary embodiment of the invention, the porous silicalayer 14 may be fabricated as follows. A first mixture of 0.3 gsurfactant and 0.6 g solvent is prepared. Polymers may be used as thesurfactant, and a mixed solvent of propanol and butanol in a ratio of1:2, may be used as the solvent. A second mixture of 5 g TEOS(Tetra-Ethyl-Ortho-Silicate), 10.65 g solvent and 1.85 g HCL is thenprepared.

The second mixture is stirred for approximately 1 hour. 2.1 g of thesecond mixture is mixed with the first mixture, forming a third mixture.The third mixture is coated on a substrate, such as a glass substrate,used as the front substrate. Usable coating methods include spincoating, spray coating, roll coating and the like. The spin coating maybe performed at 2000 rpm for 30 seconds. Next, the resulting structureis aged at room temperature for approximately 24 hours or at 40-50° C.for approximately 5 hours. In order to form absorption holes, firing isperformed on the resulting structure at an oven maintained atapproximately 400° C. for approximately 2 hours so that the polymer isburnt. The formed porous silica layer has a thickness of approximately7000°. The above-described process is repeated, thereby forming a thinfilm having a thickness of approximately 3.5 μm. Values indicating theamount of materials as described above are only used to indicate theratios thereof in the mixture, and it is recognized that specific valuesmay be adjusted accordingly.

The thus-formed porous silica layer 14 includes large absorption holes14 b in its structure, as shown in FIG. 2. While each of the absorptionholes 14 b is generally 2˜30 nm in diameter, the diameter may beadjusted by adjusting the size of the polymer used in the first mixture.The density of the absorption holes 14 b formed in the porous silicalayer 14 may be approximately 80% of the area (e.g. 80% of the area ofthe porous silica layer 14 is occupied by absorption holes 14 b). Asdescribed above, the porous silica layer 14 may be formed by spincoating, spray coating, or roll coating, and may have high mechanicaland thermal stability. Also, the formation process of the porous silicalayer 14 may be relatively easily controlled.

FIGS. 3A through 3D illustrate steps in a method of manufacturing asingle organic EL display device according to an exemplary embodiment ofthe present invention. As shown in FIG. 3A, a rear substrate 31 havingan organic EL portion 32 is prepared. Then as described above, a poroussilica layer 34 is coated on the inner surface of a front substrate 33,as shown in FIG. 3B. The front substrate 33 coated with the poroussilica layer 34 is cleaned to remove foreign matter and organic materialon its surface, and is left in a vacuous oven maintained at 150° C. forapproximately 1 hour for desorption of moisture absorbed into the poroussilica layer 34. Thereafter, a sealant 35 is coated outside the organicEL portion disposed on at least one of the rear substrate 31 and thefront substrate 33, as shown in FIG. 3C, using a screen printer or adispenser. As shown in FIG. 3D, the front substrate 33 and the rearsubstrate 31 are assembled in an assembly chamber.

In addition, an internal space 36 defined by the front and rearsubstrates of the thus-formed organic EL device may be made. Internalspace 36 may be vacuous or filled with an inert gas. The sealant 35 maybe cured using UV rays, visible light and/or heat after assembling thefront substrate 33 and the rear substrate 31.

FIGS. 4A through 4E are cross-sectional views of steps in a method ofmanufacturing a plurality of organic EL display devices according to anexemplary embodiment of the invention. First, a rear substrate 41 havinga plurality of organic EL portions 42 is prepared. A porous silica layer44 is coated on the inner surface of a front substrate 43 by theabove-described method, as shown in FIG. 4B. A sealant 45 is coatedoutside each of the plurality of organic EL portions disposed on atleast one of the rear substrate 41 and the front substrate 43, as shownin FIG. 4C. The rear substrate 41 and the front substrate 43 areassembled to each other, as shown in FIG. 4D, forming a panel having aplurality of organic EL devices mounted thereon. The panel may then becut, as shown in FIG. 4E, to provide individual organic EL devices. Aswith the manufacture of a single organic EL device, an internal space 46defined by the front and rear substrates 43 and 41 may be made. Theinternal space 46 may be vacuous or filled with an inert gas The sealant45 may be cured using UV rays, visible light and/or heat.

FIG. 5 is a flow diagram illustrating a method of manufacturing anorganic EL display device according to an exemplary embodiment of thepresent invention.

Porous silica is prepared by the above-described method (step S1). Anorganic EL portion is formed on a rear substrate (step S2). A frontsubstrate is prepared (step S3), and a porous silica layer is formed onthe prepared front substrate (step S4). A sealant is coated on eitherthe front substrate or the rear substrate (step S5). The rear substrateand the front substrate are assembled (step S6). An internal spacedefined by the front substrate and the rear substrate is made vacuous orfilled with an inert gas (step S7). The sealant is cured using UV rays,visible light and/or heat (step S8). A panel having a plurality oforganic EL devices is cut (step S9).

According to the present invention, a 3 cm by 4 cm sized, organic ELdevice having absorbing material of about 3.5 μm thickness may beproduced. The absorbing material can absorb several to several tens ofmilligrams of moisture depending on the density of the absorbingmaterial. The absorption level is not inferior to that of a typicaldesiccant, such as CaO or BaO, and the encapsulation effect can beensured for approximately 30,000 to approximately 50,000 hours whilemaintaining the transparency of the substrate of the organic EL devicehaving the absorbing material.

As described above, the organic EL device may have a transparentmoisture-absorbing layer made of porous silica. According to anembodiment of the present invention, since the substrate used forencapsulation is transparent, it can be used for a front emission typedisplay.

Also, as it is not necessary to form a separate groove in the frontsubstrate to be used as an encapsulation substrate, the manufacturingprocess may be simplified, thereby reducing the processing cost and thematerial cost.

FIG. 6 is a cross-sectional view of an organic EL display deviceaccording to an exemplary embodiment of the present invention. Referringto FIG. 6, an inorganic protection layer 17 is disposed on the secondelectrode of the organic EL portion 12.

Further, since the front substrate is relatively thin, the overallvolume of the organic EL display device is reduced, thereby achievingminiaturization of the organic EL device.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those of ordinary skill in the artthat changes may be made in these elements without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

What is claimed is:
 1. An organic electroluminescent display device,comprising: a rear substrate; an organic electroluminescent portiondisposed on a surface of the rear substrate, the organicelectroluminescent portion comprising a first electrode, an organiclayer, and a second electrode in sequence; a front substrate coupled tothe rear substrate at an internal surface of the front substrate to sealan internal space in which the organic electroluminescent portion isaccommodated, thereby isolating the organic electroluminescent portionfrom the outside; a transparent moisture-absorbing layer coated on theinternal surface of the front substrate; and a sealant disposed betweenthe rear substrate and the transparent moisture-absorbing layer tocouple the front substrate and the rear substrate.
 2. The organicelectroluminescent display device of claim 1, wherein the transparentmoisture-absorbing layer comprises absorption holes.
 3. The organicelectroluminescent display device of claim 2, wherein each of theabsorption holes has a diameter in a range of about 0.5 nm to about 100nm.
 4. The organic electroluminescent display device of claim 2, whereinthe transparent moisture-absorbing layer has a thickness range of about100 nm to about 50 μm.
 5. The organic electroluminescent display deviceof claim 4, wherein each of the absorption holes has a diameter in arange of about 0.5 nm to about 100 nm.
 6. The organic electroluminescentdisplay device of claim 1, wherein: the first electrode of the organicelectroluminescent portion comprises a transparent electrode; and thesecond electrode of the organic electroluminescent portion comprises areflection-type electrode.
 7. The organic electroluminescent displaydevice of claim 1, wherein: the first electrode of the organicelectroluminescent portion comprises a reflection-type electrode; andthe second electrode of the organic electroluminescent portion comprisesa transparent electrode.
 8. The organic electroluminescent displaydevice of claim 1, wherein an inorganic protection layer is disposed onthe second electrode.
 9. The organic electroluminescent display deviceof claim 8, wherein the inorganic protection layer comprises one of ametal oxide and a metal nitride.
 10. The organic electroluminescentdisplay device of claim 1, wherein the internal space defined by thefront substrate and the rear substrate is configured to be vacuous. 11.The organic electroluminescent display device of claim 1, wherein theinternal space defined by the front substrate and the rear substrate isconfigured to be filled with an inert gas.
 12. The organicelectroluminescent display device of claim 1, wherein the frontsubstrate comprises one of a glass substrate and a transparent plasticsubstrate.
 13. The organic electroluminescent display device of claim12, wherein a protection layer for protecting the front substrate frommoisture is disposed on one of the internal surface and an outer surfaceof the front substrate.